FTOK(3) 						     Linux Programmer's Manual							   FTOK(3)

NAME

       ftok - convert a pathname and a project identifier to a System V IPC key

SYNOPSIS

       #include <sys/types.h>
       #include <sys/ipc.h>

       key_t ftok(const char *pathname, int proj_id);

DESCRIPTION

       The  ftok()  function  uses the identity of the file named by the given pathname (which must refer to an existing, accessible file) and the
       least significant 8 bits of proj_id (which must be nonzero) to generate a key_t type System V IPC key, suitable	for  use  with	msgget(2),
       semget(2), or shmget(2).

       The  resulting  value  is  the  same for all pathnames that name the same file, when the same value of proj_id is used.	The value returned
       should be different when the (simultaneously existing) files or the project IDs differ.

RETURN VALUE

       On success, the generated key_t value is returned.  On failure -1 is returned, with errno indicating the error as for  the  stat(2)  system
       call.

ATTRIBUTES

       For an explanation of the terms used in this section, see attributes(7).

       +----------+---------------+---------+
       |Interface | Attribute	  | Value   |
       +----------+---------------+---------+
       |ftok()	  | Thread safety | MT-Safe |
       +----------+---------------+---------+
CONFORMING TO

       POSIX.1-2001, POSIX.1-2008.

NOTES

       On some ancient systems, the prototype was:

	   key_t ftok(char *pathname, char proj_id);

       Today,  proj_id	is an int, but still only 8 bits are used.  Typical usage has an ASCII character proj_id, that is why the behavior is said
       to be undefined when proj_id is zero.

       Of course, no guarantee can be given that the resulting key_t is unique.  Typically, a best-effort attempt combines the given proj_id byte,
       the  lower  16 bits of the inode number, and the lower 8 bits of the device number into a 32-bit result.  Collisions may easily happen, for
       example between files on /dev/hda1 and files on /dev/sda1.

SEE ALSO

       msgget(2), semget(2), shmget(2), stat(2), svipc(7)

COLOPHON

       This page is part of release 4.15 of the Linux man-pages project.  A description of the project, information about reporting bugs, and  the
       latest version of this page, can be found at https://www.kernel.org/doc/man-pages/.

GNU
								    2015-08-08								   FTOK(3)